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Numerical simulations are required to thermophysically characterize Oxia Planum, the landing site of the mission ExoMars 2022. A drilling system is installed on the ExoMars rover, and it will be able to analyze down to 2 meters in the subsurface of Mars. The spectrometer Ma_MISS (Mars Multispectral Imager for Subsurface, Coradini and Da Pieve, 2001) will investigate the lateral wall of the borehole generated by the drill, providing hyperspectral images. It is not fully clear if water ice can be found in the subsurface at Oxia Planum. However, Ma_MISS has the capability to characterize and map the presence of possible ices, in particular water ice. We performed simulations of the subsurface temperatures by varying the thermal inertia, and we quantified the effects of self-heating. Moreover, we quantified the heat released by the drilling operations, by exploring different frictional coefficients and angular drill velocities, in order to evaluate the lifetime of possible water ice.

Ceres is the largest body in the Main Belt, and it is characterized by a large abundance of water ice in its interior. This feature is suggested by its relatively low bulk density (2162 kg m−3), while its partial differentiation into a rocky core and icy crust is suggested by several geological and geochemical features: minerals and salts produced by aqueous alteration, icy patches on the surface, and lobate morphology interpreted as surface flows. In this work, we explore how the composition can influence the characteristics of thermal convection in the crust of Ceres. Our results suggest that the onset of thermal convection is difficult and when it occurs, it is short lived, which could imply that Ceres preserved deep liquid until present, as recently suggested by the work of Castillo-Rogez et al. Moreover, cryovolcanism could be driven by diapirism (chemical convection) rather than thermal convection.

We analyzed the surface of Vesta at visible wavelengths, using the data of the Visible and InfraRed mapping spectrometer (VIR) on board the Dawn spacecraft. We mapped the variations of various spectral parameters on the entire surface of the asteroid, and also derived a map of the lithology. We took advantage of the recent corrected VIR visible data to map the radiance factor at 550 nm, three color composites, two spectral slopes, and a band area parameter relative to the 930 nm crystal field signature in pyroxene. Using the howardite-eucrite-diogenite (HED) meteorites data as a reference, we derived the lithology of Vesta using the variations of the 930 nm and 506 nm (spin-forbidden) band centers observed in the VIR dataset. Our spectral parameters highlight a significant spectral diversity at the surface of Vesta. This diversity is mainly evidenced by impact craters and illustrates the heterogeneous subsurface and upper crust of Vesta. Impact craters also participate directly in this spectral diversity by bringing dark exogenous material to an almost entire hemisphere. Our derived lithology agrees with previous results obtained using a combination of infrared and visible data. We therefore demonstrate that it is possible to obtain crucial mineralogical information from visible wavelengths alone. In addition to the 506 nm band, we identified the 550 nm spin-forbidden one. As reported by a laboratory study for synthetic pyroxenes, we also do not observe any shift of the band center of this feature across the surface of Vesta, and thus across different mineralogies, preventing use of the 550 nm spin-forbidden band for the lithology derivation. Finally, the largest previously identified olivine rich-spot shows a peculiar behavior in two color composites but not in the other spectral parameters., Comment: 23 pages, 11+7 figures

The identification of NH4-bearing phyllosilicates on Ceres poses the question on the NH4-carrier phase(s) and in this study we describe the laboratory production and IR spectroscopic measurements of a suite of ten NH4-phyllosilicates, starting from the corresponding NH4-free minerals. For each mineral, we prepared three types of powder samples: raw (R), ammoniated (A), and leached (L). All samples have been spectrally characterized by means of visible/infrared spectroscopy in the INAF-IAPS laboratories with the FieldSpec Pro in the 0.35–2.5 µm range, and with the FT-IR, using a Vertex 80 spectrometer operating in the range of 2–14 µm. The samples were also measured with the SPectral IMager, an imaging spectrometer operating in the spectral range 0.2–5.1 µm, which is a replica of the VIR spectrometer on-board Dawn spacecraft. Reflectance spectra of the ammoniated clays show bands near 1.56 µm, 2.05 µm, 2.12 µm, 3.06 µm, 3.25 µm, 3.55 µm, 4.2 µm, 5.7 µm and 7.0 µm that are related to the presence of nitrogen complexes. Treatment of phyllosilicates with ammonia shows that different minerals behave in different ways: NH4+ ions are easily accepted by the smectites, while other non-expandable structures do not accept these ions. The obtained results can be used to better constrain the NH4-bearing species present on Ceres and, possibly, other bodies of the solar system.

At the beginning of the Ceres investigation, the Dawn-NASA mission discovered a large bright spot (BS) in the Occator crater floor. Several other smaller bright spots were discovered during the following phases of the mission. In this paper, a complete survey for the detection of BS on the Ceres surface have been made by using the hyperspectral data acquired by Visible and Infrared Mapping Spectrometer (VIR). The hyperspectral images span the spectral range from 0.2 to 5 μm, by using two channel, the VIS channel with a spectral sampling of 1.8 nm and a IR channel with a spectral sampling of 9.8 nm. Finally a catalogue of 92 BS has been compiled and their compositional properties have been examined. In particular, five spectral parameters have been applied to perform the analysis: the photometrically corrected reflectance and four band depths, related to spectral absorptions at 2.7 μm (OH fundamental indicative of phyllosilicates), at 3.05 μm (due to ammoniated clays), at 3.4 and 4.0 μm (carbonate overtones). The 90% of BS are impact-related features (ejecta, crater rim, crater floor, crater wall). The two brightest BS, Cerealia and Vinalia Faculae, are located on the Occator crater floor. Most of BSs show features similar to the average Ceres surface, which has low reflectance and is composed of Mg-phyllosilicates and ammoniated clays, with a reduced abundance of Mgsbnd Ca carbonates. Cerealia and Vinalia Faculae are a peculiar BS family, with a high abundance of Na-carbonates and Al-rich phyllosilicates. Oxo and a companion bright spot represents a third category, depleted in phyllosilicates and with a high to moderate albedo. Carbonate composition ranges from Mg/Ca to Na components. Haulani, Ernutet, Kupalo, and other two BS's represent another group, with intermediate properties between the typical BS and the Oxo family: they are moderately rich in carbonates and slightly depleted in Mg- and ammoniated phyllosilicates. The four families probably explain a single evolutionary path followed by the BS from the formation to their maturity: initially the very fresh bright spots would possess characteristics similar to Cerealia and Vinalia Faculae; with time, salts and OH volatilize and a light mixing with surrounding material would produce Oxo-like BS's; additional strong mixing would form Haulani-like BS, which finally become a typical bright spots.

Occator Crater on dwarf planet Ceres hosts the so-called faculae, several areas with material 5 to 10 times the albedo of the average Ceres surface: Cerealia Facula, the brightest and largest, and several smaller faculae, Vinalia Faculae, located on the crater floor. The mineralogy of the whole crater is analyzed in this work. Spectral analysis is performed from data of the VIR instrument on board the Dawn spacecraft. We analyse spectral parameters of all main absorption bands, photometry, and continuum slope. Because most of the absorption features are located in a spectral range affected by thermal emission, we developed a procedure for thermal removal. Moreover, quantitative modeling of the measured spectra is performed with a radiative transfer model in order to retrieve abundance and grain size of the identified minerals. Unlike the average Ceres surface that contains a dark component, Mg-Ca-carbonate, Mg-phyllosilicates, and NH4-phyllosilicates, the faculae contain mainly Na-carbonate, Al-phyllosilicates, and NH4-chloride. The present work establishes unambiguously the presence of NH4-chloride thanks to the high-spatial resolution data. Vinalia and Cerealia Faculae show significant differences in the concentrations of these minerals, which have been analyzed. Moreover, heterogeneities are also found within Cerealia Facula that might reflect different deposition events of bright material. An interesting contrast in grain size is found between the center (10-60 μm) and the crater floor/peripheral part of the faculae (100-130 μm), pointing to different cooling time of the grains, respectively faster and slower, and thus to different times of emplacement. This implies the faculae formation is more recent than the crater impact event, consistent with other observations reported in this special issue. For some ejecta, we derived larger concentrations of minerals producing the absorption bands, and smaller grains with respect to the surrounding terrain. This may be related to heterogeneities in the material pre-existent to the impact event.

An essential part of the Exomars 2022 payload is the Mars Multispectral Imager for Subsurface Studies (Ma_MISS) experiment hosted by the drill system. Ma_MISS is a visible and near-infrared (0.4–2.3 μm) miniaturized spectrometer with an optical head inside the drill tip capable of observing the drill borehole with a spatial resolution of 120 μm. Here we report on how the Ma_MISS hyperspectral information provides in situ investigation of the subsurface at very fine resolution, prior to the collection of the samples that will be manipulated and crushed for further analysis by the analytical laboratory on the rover. Ma_MISS is the instrument that will closely investigate the subsurface mineralogical characteristics in its original geologic context at depths never reached before in Mars exploration. Ma_MISS recognizes all the major spectral features of the clays, basaltic, and minor phases expected at the ExoMars landing site, Oxia Planum. The high spatial resolution on the borehole wall is such that single grains of about 100 μm can be distinguishable in the assemblage of minerals observed by Ma_MISS. The spatial distribution of the mineralogies within the borehole walls is associated with the rocks and the processes that put these materials in place and possibly altered them with time, characterizing the habitats found in the stratigraphic record, indicating which ones are the most suitable to have held or to be holding nowadays traces of life.

We present new spectral observations using ground-based telescopes of 23 putative V-type asteroids, selected according to colour surveys in the visible from the Moving Objects Catalogue of the Sloan Digital Sky Survey and near-infrared from the Moving Objects VISTA catalogue. 10 asteroids are orbiting in the middle main belt, while five in the outer part of the main asteroid belt. For the observed asteroids, we assign a taxonomical classification and confirm the basaltic nature for 16 of them. The high-quality spectra in the UV range, obtained with the X-Shooter spectrograph at ESO, allowed the identification of the Fe2+ forbidden transition of pyroxene for 10 asteroids. This band is centred at 506.5 nm, and it is diagnostic of the Ca-content in the pyroxene form. We determined a low Fe-content composition for asteroids (2452) Lyot, (5758) Brunini, (7675) Gorizia, (9197) Endo, (22308) 1990 UO4, (36118) 1999 RE135, (66905) 1999 VC160, and (189597) 2000 WG119, and a composition more rich in Fe for asteroids (75661) 2000 AB79 and (93620) 2000 UQ70. We also present a dynamical investigation of V-type asteroids in the middle and outer main belt. The principal finding of these simulations is that the middle and outer V-types are more likely to be associated with some families, which were considered as possibly originated from the break up of a partially or totally differentiated parent body by diverse studies. This reinforces the hypothesis that the identified V-type in the region were not originated from (4) Vesta and that the number of differentiated objects in the middle and outer main belt must have been much larger than previously assumed.

We study the surface of Ceres at visible wavelengths, as observed by the Visible and InfraRed mapping spectrometer (VIR) onboard the Dawn spacecraft, and analyze the variations of various spectral parameters across the whole surface. We also focus on several noteworthy areas of the surface of this dwarf planet. We made use of the newly corrected VIR visible data to build global maps of a calibrated radiance factor at 550 nm, with two color composites and three spectral slopes between 400 and 950 nm. We have made these maps available for the community via the Aladin Desktop software. Ceres surface shows diverse spectral behaviors in the visible range. The color composite and the spectral slope between 480 and 800 nm highlight fresh impact craters and young geologic formations of endogenous origin, which appear bluer than the rest of the surface. The steep slope before 465 nm displays very distinct variations and may be a proxy for the absorptions caused by the $O_2^{-}$ -> $Fe^{3+}$ or the $2Fe^{3+}$ -> $Fe^{2+} + Fe^{4+}$ charge transfer, if the latter are found to be responsible for the drop in this spectral range. We notice several similarities between the spectral slopes and the abundance of phyllosilicates detected in the infrared by the VIR, whereas no correlation can be clearly established with carbonate species. The region of the Dantu impact crater presents a peculiar spectral behavior (especially through the color and the spectral slope before 465 nm) suggesting a change in composition or in the surface physical properties that is not observed elsewhere on Ceres., 22 pages, 14 + 5 figures. Published online on Astronomy and Astrophysics on 07-10-2020

The European Space Agency’s Rosetta mission1 has acquired unprecedented measurements of the surface of the nucleus of comet 67P/Churyumov–Gerasimenko (hereafter, 67P), the composition of which, as determined by in situ and remote-sensing instruments, including the VIRTIS instrument2, seems to be an assemblage of ices, minerals and organic material3. We performed a refined analysis of infrared observations of the nucleus of 67P carried out by the VIRTIS-M hyperspectral imager. We find that the overall shape of the infrared spectrum of 67P is similar to that of other carbon-rich outer Solar System objects, suggesting a possible genetic link with them. More importantly, we also confirm the complex spectral structure of the wide 2.8–3.6 µm absorption feature populated by fainter bands. Among these, we unambiguously identify the presence of aliphatic organics by their ubiquitous 3.38 µm, 3.42 µm and 3.47 µm bands. This infrared detection of aliphatic species on a cometary surface has strong implications for the evolutionary history of the primordial Solar System and is evidence that comets provide an evolutionary link between interstellar material and Solar System bodies4. A refined analysis of infrared observations of comet 67P/Churyumov–Gerasimenko from the VIRTIS instrument on board the Rosetta spacecraft has revealed the presence of aliphatic organic molecules on the comet nucleus.

We present an analysis of the areal distribution of spectral parameters derived from the VIR imaging spectrometer on board NASA/Dawn spacecraft. Specifically we studied the Occator quadrangle of Ceres, which is bounded by latitudes 22°S to 22°N and longitudes 214°E to 288°E, as part of the overall study of Ceres’ surface composition reported in this special publication. The spectral parameters used are the photometrically corrected reflectance at 1.2 µm, the infrared spectral slope (1.1–1.9 µm), and depths of the absorption bands at 2.7 µm and 3.1 µm that are ascribed to hydrated and ammoniated materials, respectively. We find an overall correlation between 2.7 µm and 3.1 µm band depths, in agreement with Ceres global behavior, and band depths are shallower and the spectral slope is flatter for younger craters, probably due to physical properties of regolith such as grain size. Spectral variations correlated with the tali geological unit also suggest differences in physical properties. The deepest band, indicating enrichment of ammoniated phyllosilicates, are associated with ejecta generated by impacts that occurred in southern quadrangles. The most peculiar region of this quadrangle is the Occator crater (20°N 240°E). The internal crater area contains two faculae, which are the brightest areas on Ceres due to exposure of sodium carbonates, and by two types of ejecta, dark and bright, with different spectral properties, probably due to different formation, evolution or age.

This article presents the spectral parameter maps used in this Surface Composition of Ceres Special Issue. The definition and use of spectral parameters has always played a fundamental role in understanding the properties and composition of a planetary surface. Mapping proper spectral parameters shows the global mineralogical diversity across Ceres. In this work, we discuss the production process of Ceres spectral parameter maps derived by the data of the Visible and Infrared mapping spectrometer (VIR) onboard NASA’s Dawn mission. We describe the data processing of the VIR spectra and the procedure to retrieve the geometries (latitude, longitude and illumination angles) of the acquired data. Spectra and geometries are used to project and mosaic this data to produce Geographic Information System-compatible spectral parameters maps of Ceres. An overview of the variability of the data across the quadrangles is given, addressing the specific analysis to each quadrangle mapping paper included in this special issue.

The dwarf planet Ceres is a heavily cratered rocky body, and complex craters with a central peak are widely observed on its surface. These types of craters form when a large body impacts the surface, generating extreme temperatures and pressures. During the impact event a large volume of rock is raised from the subsurface and a central uplift is formed. The material composing the central uplift is called crater central peak material (ccp) and the spectral analysis of such geologic areas can provide information about the composition of Ceres’ subsurface. Reflectance spectra of 32 ccps, acquired by the VIR spectrometer on board the NASA/Dawn spacecraft, were analyzed and shows absorption bands located at about 2.7, 3.1, 3.4 and 4.0 µm which are also common on the Cerean surface. These absorptions are related, respectively, to Mg-phyllosilicates, NH4-phyllosilicates and Mg/Ca-carbonates. The spectral parameters considered in this work are: spectral slopes estimated between 1.2 µm and 1.9 µm, band depths at 2.7-, 3.1-, 3.4- and 4.0-µm, and band centers near 4.0-µm. The ccps spectral parameters were analyzed in conjunction with other Cerean parameters, such as the estimated depth of excavation of the material composing the central peak, in order to search for correlations and information about Ceres’ subsurface. Central peak material located polewards show stronger 2.7- and 3.1-µm band depths with respect to those at the equatorial region, suggesting that subsurface deposits closer to poles are probably richer in Mg- and NH4-phyllosilicates. The 3.4-µm spectral feature is also deeper in ccps located at poleward latitudes, similar to the phyllosilicates. Conversely, the 4.0-µm band does not show this trend with latitude. An increase in both 3.1- and 3.4-µm band depths with the estimated depth of excavation indicates that the spectral feature at 3.4-µm is the result of different contributions from carbonates and NH4-phyllosilicates, as expected. However, depending on their relative influence, the shape of the 3.4-µm spectral feature can vary. Phyllosilicates and carbonates are the resulting products of aqueous alteration of chondritic material and, given the increasing abundance of such minerals (in particular ammoniated phyllosilicates) with depth of excavation, it is likely that our investigation involved subsurface layers nearby the boundary between the volatile-rich crust and the silicate-rich mantle. Na-carbonate is found in the crater central peak material of Ernutet, Haulani and Ikapati, characterized by an estimated depth of excavation of about 6–9 km, where deposits of sodium carbonates could be locally present.

Impact craters of different geological ages, sizes and morphologies are not only the most obvious surface features on Ceres’ surface. The investigation of their spectral properties in combination with Ceres’ geology and topography reveals not only lateral compositional variations in Ceres’ surface material but also possible stratigraphic differences within Ceres’ crust. Spectral properties of impact craters with different ages do show distinct trends implying variations with increasing exposure duration of the impact material onto Ceres’ surface. Local concentrations of H2O ice and carbonates are associated with the youngest, either recently emplaced or excavated, surface deposits. On the contrary, regionally higher amounts of ammoniated phyllosilicates originate from deeper regions of Ceres’ crust and strengthen the theory of ammonia being a primordial constituent of Ceres. The blue spectral slope, clearly associated with relatively weak absorptions of OH-bearing and/or ammoniated phyllosilicates, is limited to fresh impact material. Either, the blue spectral slope diminishes slowly with increasing geologic age due to space weathering processes, or shortly as a result of gravitation-induced slumping, forming a fine and loosely consolidated regolith.

We studied the distribution in the Urvara–Yalode region of Ceres (latitudes 21–66°S, longitudes 180–360°E) of main spectral parameters derived from the VIR imaging spectrometer onboard the NASA/Dawn spacecraft, as an overall study of Ceres mineralogy reported in this special issue. In particular, we analyzed the distribution of reflectance at 1.2 µm, band depth at 2.7 and 3.1 µm, ascribed to magnesium and ammoniated phyllosilicates, respectively. Whereas the average band depths of this region are lower than eastern longitudes, reflecting the E-W dichotomy of abundance of phyllosilicates on Ceres, spectral variations inside this region are observed in the following units: (a) the central peak of the Urvara crater (45.9°S, 249.2°E, 170 km in diameter), showing a deep 3.1 µm band depth, indicating an ammonium enrichment; (b) the cratered terrain westwards of the Yalode basin (42.3°S, 293.6°E, 260 km in diameter), where absorption bands are deeper, probably due to absence of phyllosilicates depletion following the Yalode impact; (c) the hummocky cratered floor of Yalode and Besua (42.4°S, 300.2°E) craters, characterized by lower albedo and band depths, probably due to different roughness; (d) Consus (21°S 200°E) and Tawals (39.1°S, 238°E) craters, whose albedo and band depths decreasing could be associated to different grain size or abundance of dark materials. Twenty-two small scale (i.e., lower than 400 m) bright spots are observed: because their composition is similar to the Ceres average, a strong mixing may have occurred since their formation.

Ceres has been explored by NASA/Dawn spacecraft, which allowed for the discovery of the main mineralogical and compositional characteristics of Ceres' surface. Here, we use mainly data from the Visible and InfraRed imaging spectrometer (VIR) in order to investigate the main spectral characteristics of the quadrangle Ac-H-2 Coniraya, one of the 15 quads in which Ceres' surface has been divided. Coniraya quadrangle is characterized by the presence of mostly highly degraded impact craters of diameters between 50 and 200 km and clusters of small to midsize impact craters. Although the composition over the quadrangle appears to be quite uniform, significant differences have been detected between different craters by spectral parameters analysis and spectral modeling. Ernutet crater presents two regions with very peculiar band at 3.4 μm, typical of organics aliphatic material. One region result to be correlated with larger amount of carbonates, the other region does not present such correlation. Ikapati crater shows strong absorption bands at 4.0 μm, indicating the presence of Na-carbonates in the floor and ejecta. Ikapati, Gaue and other craters present smaller spectral features of NH4 and/or OH stretching, suggesting a volatile depletion process induced by the heating of the impact event.

This paper focuses on the identification and distribution of compositional units and their stratigraphic relationships in the Fejokoo quadrangle of Ceres (Ac-5) located between 21–66°N and 270–360°E and named after one of its prominent and well-preserved impact craters, Fejokoo (centered at 26°N and 312°E). In this quadrangle, we observed that hydroxylated- (OH-rich) and ammoniated- (NH4-rich) phyllosilicates are present everywhere, in various abundances; low abundance is observed on bright terrains and higher abundances are observed on lobate materials associated with craters. Carbonates are mostly correlated with the high-albedo areas surrounding Oxo (359.7°E, 42.2°N) and other major craters, and are mixed with Ceres’ most common surface composition type (i.e. low albedo, phyllosilicate-rich material). There are a few locations where carbonates and phyllosilicates co-exist, indicating a range of geological or chemical processes produced them in co-existence. No correlation between the surface composition and the age of the craters was found. Instead, the composition observed on impact craters depends on the size of the impact and the composition of the different stratigraphic layers excavated. The compositional interpretation inferred from Dawn's visible-infrared spectrometer data of the Fejokoo quadrangle is consistent with the presence of an internal ocean that produced carbonates and phyllosilicates via aqueous alteration of minerals.

Mineralogical maps of the Ac-H-11 Sintana and the Ac-H-12 Toharu quadrangles of the dwarf planet Ceres were produced in order to access the composition of this planetary body. We used data from NASA's Dawn spacecraft, in particular the spectra returned by VIR, the imaging spectrometer on board. Different spectral parameters in the infrared range have been computed to study the composition of this portion of Ceres’ surface and its large and small scale variability. We studied the variation and distribution of the phyllosilicate bands at 2.73 µm and 3.07 µm, the reflectance at 1.2 µm, and the overall spectrum in specific locations. We did not observe variations of the center of the bands at 2.73 µm and 3.07 µm, with the exception of a few pixels in the Kupalo crater. We found that this southern region, extending from 0° to 180° and from 21°S to 66°S, show an overall increase of phyllosilicate band intensity from the equatorial areas to the southern areas. Superimposed to the large-scale trend, we observe many smaller localized variations of band intensity. The observed variations can indicate large and small-scale heterogeneities in the abundance of the different species in the Ceres subsurface. However, the small-scale variation that is mostly associated with young craters, can be also due to processes related with impacts, such as de-hydration or delivery of exogenous material that, mixed with the original surface, could change the band intensity. Several craters, such as Kupalo and Juling, show a different composition with respect to the background, displaying water ice and sodium carbonates.

Quadrangle Ac-H-08 Nawish is located in the equatorial region of Ceres (Lat 22°S-22°N, Lon 144°E- 216°E), and it has variable mineralogy and geology. Here, we report on the mineralogy using spectra from the Visible and InfraRed (VIR) mapping spectrometer onboard the NASA Dawn mission. This quadrangle has two generally different regions: the cratered highlands of the central and eastern sector, and the eastern lowlands. We find this dichotomy is also associated with differences in the NH4-phyllosilicates distribution. The highlands, in the eastern part of the quadrangle, appear depleted in NH4-phyllosilicates, conversely to the lowlands, in the north-western side. The Mg-phyllosilicates distribution is quite homogeneous across Nawish quadrangle, except for few areas. The 2.7 µm band depth is lower in the south-eastern part, e.g. in the Azacca ejecta and Consus crater ejecta, and the band depth is greatest for the Nawish crater ejecta, and indicates the highest content of Mg-phyllosilicates of the entire quadrangle. Our analysis finds an interesting relationship between geology, mineralogy, topography, and the age in this quadrangle. The cratered terrains in the highlands, poor in NH4 phyllosilicates, are older (2 Ga). Conversely, the smooth terrain, such as with Vindimia Planitia, is richer in ammonia-bearing phyllosilicates and is younger (1 Ga). At the local scale, Ac-H-8 Nawish, displays several interesting mineralogical features, such as at Nawish crater, Consus crater, Dantu and Azzacca ejecta, which exhibit localized Na-carbonates deposits. This material is superimposed on the cratered terrains and smooth terrains and shows the typical depletion of phyllosilicates, already observed on Ceres in the presence of Na-carbonates.

Chlorinated compounds have been recently identified or suggested to exist in a number of planetary bodies such as Ceres, Europa, Ganymede, Enceladus and Mars, on the basis of remote sensing and in-situ measurements as well as Earth-based telescopic observations. Sodium and magnesium-bearing chlorinated compounds with different levels of hydration have been suggested to reach the surface of these bodies through ascending flows from the interior; thus, such materials could be geochemically related to the putative presence of subsurface liquid reservoirs and could bring precious information about those layers' salty composition. Laboratory spectroscopic data of chlorinated salts carried out at temperatures representative of real planetary bodies, fundamental to correctly interpret the observational data, are currently missing or incomplete. Here we present laboratory reflectance spectra of two hydrated magnesium chlorides, namely MgCl2•2H2O and MgCl2•6H2O, measured at three different grain sizes and at twelve temperature values in the range 80÷295 K. All spectra have been measured in the visible and infrared spectral range 0.5÷4.7 μm. We examined the absorption features and related spectral parameters as a function of both temperature and grain size. These reflectance spectra, as far as the infrared range beyond 2.5 μm is concerned, are the first measured and published at cryogenic temperatures, therefore these data may prove very useful for the interpretation and modeling of remote sensing spectral data from planetary missions. In particular, this new dataset will be helpful in applying spectral unmixing models to past and future observations of some icy satellites, Mars, Ceres, and possibly other Solar System bodies.

The surface mineralogy of dwarf planet Ceres appears to be dominated by products of rock–fluid interactions, such as phyllosilicates—some of which are NH4-bearing—and carbonates1–3. Elemental concentrations derived from the inferred mineral mixing fractions, however, do not match measurements of H, C, K and Fe on Ceres4. A complicating factor in assessing Ceres’s unique surface composition is the secular accretion of asteroids typical of chondritic compositions. Here we show that Ceres’s mineral and elemental data can be explained by the presence of carbonaceous chondritic-like materials (~50–60 vol%), possibly due to infalling asteroids, admixed with aqueously altered endogenic materials that contain higher-than-chondritic concentrations of carbon. We find that Ceres’s surface may contain up to 20 wt% of carbon, which is more than five times higher than in carbonaceous chondrites. The coexistence of phyllosilicates, magnetite, carbonates and a high carbon content implies rock–water alteration played an important role in promoting widespread carbon chemistry. These findings unveil pathways for the synthesis of organic matter, with implications for their transport across the Solar System. Infrared and neutron spectroscopic observations by Dawn give contrasting results on the elemental composition of Ceres’s surface, which can be reconciled by assuming that Ceres’s surface contains ~20 wt% of carbon, coming from impacts by carbonaceous asteroids and/or generated by extensive aqueous alteration.

Since its arrival at Ceres, DAWNs Framing Camera has been imaging the dwarf planet at different altitudes, using 8 different filters. Based on these images, global clear filter mosaics, digital terrain models, and global color mosaics were produced. These datasets are basis for the derived photogeologic map of the Ac2 Coniraya quadrangle, located between 0° and 90° eastern longitude and between 20° and 40° northern latitude. Crater size frequency distribution (CSFD) measurements have been applied to derive the stratigraphic history of the identified geologic units in the Ac2 Coniraya quadrangle. Based on these investigations, we found that the Ac2 Coniraya quadrangle shows evidence for a long geologic history lasting over 3.5 Ga. Most of the identified geologic units are related to impact cratering at different periods of time. While the oldest unit identified in the Ac2 Coniraya quadrangle, the cratered terrain, shows an absolute model age (AMA) of 3.3 to 3.5 Ga, the youngest units, including fresh impact craters and lobate flows, show AMAs of < 100 Ma. The large number of different sized impact craters excavated a variety of materials with different colors and albedo, indicative of a heterogeneous crustal composition, including water or volatiles. Pits identified at Ikapati craters smooth deposits might further indicate the presence of volatiles in the subsurface. Furthermore, our mapping of the Ac2 Coniraya quadrangle shows that possible H 2 O ice in the crust is heterogeneously distributed, as lobate flows, bright spots, and pits are only found at certain locations, related to relatively fresh impact craters.

Ceres is the largest object in the main belt and is a wet body with a complex geological and chemical history. Its surface is composed of opaque materials, phyllosilicates, ammoniated-bearing minerals, carbonates, water ice, and salts. Recently, aliphatic organics, whose origin is still uncertain, have also been detected on the Ceres surface by the imaging spectrometer Visible and Infrared Spectrometer (VIR) on board Dawn. Here, using VIR spectra, acquired with a high spatial resolution (< 100 m), we have analysed the organic-rich areas, their spectral characteristics, and the associated mineralogy. The new VIR spectra in the 3.2-3.6 µm spectral range have been compared to organic standard compounds measured in the laboratory, to investigate more deeply the nature of the organic matter on Ceres. The mineralogy appears quite complex, and the organic matter is often associated with a larger amount of ammoniated phases and carbonates. The detailed spectral analysis, as well as the laboratory comparison, reveal the presence of a band at 2.99-3 μm, likely associated with organic or inorganic NH-compounds (amine or salts), and the organic matter may be characterized by a rather low abundance of oxygen atoms. Spectral models of the organic material indicate that hundreds of meters-size areas can be very rich in aliphatic organics, with an estimated organic amount larger than the quantity normally found in CC meteorites. The mineralogical context and the retrieved amounts suggest that the aliphatic organic is likely a Ceres' endogenous product, and we formulate a hypothesis for the formation and evolution of the organic matter inside Ceres.

NASA’s Dawn spacecraft acquired images and hyperspectral data of Ceres by means of FC and VIR instruments, and identified some widespread bright areas or bright spots (BS). The most peculiar BS is inside Occator crater and it is characterized by spectral properties very dissimilar from the rest of Ceres’ surface. To perform a mineralogical analysis, absorption bands in reflectance spectra must be properly isolated by removal of continuum, and related descriptors (such as band centers and band depths) can be computed. The method for continuum removal must be applicable to all Ceres spectra, relative to different areas, so that a comparison among spectral parameters can be made and mineralogical interpretation can be achieved. This work focuses on the definition of the most appropriate continuum to isolate absorption bands located at ∼3.1, ∼3.4 and ∼4.0 µm. The ∼3.1 µm feature is related to ammoniated phyllosilicates, while the ∼3.4 and ∼4.0 µm absorption bands are indicative of carbonates. Thermal emission affects the continuum for these bands in the VIR spectral range, which extends up to 5.1 µm, moreover all thermal-removed reliable data stop at 4.2 µm. This implies that the shoulder of bands at longer wavelength cannot be identified. We therefore defined alternative continua, i.e., a linear and two polynomial ones, able to describe spectra of any area (i.e. bright or dark) and regardless of spatial resolution. We found that the linear definition satisfies these requirements best. For the first time, we performed an error evaluation on band depths and band centers introduced by the applied method, which is relevant for comparison of spectral parameters of Ceres regions and to better interpret mineralogy and photometric effects.

Thermal inertia is a key information to quantify the physical status of a planetary surface; it can be retrieved by comparison between theoretical and observed temperature diurnal profiles. We have calculated the surface temperature for a set of locations on Ceres' surface with a thermophysical model that provides temperature as a function of thermal conductivity and roughness, and we have determined the values of those parameters for which the best fit with the observed data is obtained. The observed temperatures have been retrieved form spatially-resolved data from the Dawn mission. In our previous work [Rognini et al., 2019], we have found that the average thermal inertia for the overall surface of Ceres is low (from 1 to 15 to 60 ​J ​m−2 ​s−½ K−1), as expected according to the general trend observed in the Solar System for atmosphere-less bodies, while the thermal inertia of the very bright faculae found in the floor of the Occator crater could not be well defined. Using more recently acquired VIR high resolution data we find that the central part of the Cerealia facula displays a thermal anomaly ( ~ 10 K above the average) compatible with a higher thermal inertia with respect to the surrounding regions, while the Vinalia facula does not display any consequently could have a grain size comparable with the Ceres’ surface average.

The origin of basaltic asteroids found in the middle and outer main belt is an open question. These asteroids are not dynamically linked to the Vesta collisional family and can be the remnants of other large differentiated asteroids present in the early phases of the main belt but destroyed long ago. Spectroscopic investigation of some V-type asteroids in the middle-outer belt, classified as such by their SLOAN photometric colours (Ivezić et al.) and WISE albedos (Masiero et al.), has revealed that their spectra are more similar to other taxonomic classes, like -Q, R, S, or A (Jasmim et al. and Oszkiewicz et al.). Here, we report about the observation, in the near-infrared spectral range, of five V-type asteroids located beyond 2.5 au. These observations allowed us to infer their taxonomic classification. Two asteroids, (21238) Panarea (observed in a previous campaign but here included for comparison) and (105041) 2000 KO41, confirm their basaltic nature. For asteroids (10800) 1992 OM8 and (15898) Kharasterteam a taxonomic classification is more uncertain, being either Q- or S-type. Asteroid (14390) 1990 QP10 classification is difficult to ascribe to the known taxonomic classes, maybe due to the low-quality spectrum. Further observations are desirable for this asteroid.

The surface and internal structure of Ceres show evidence of a global process of aqueous alteration, indicating the existence of an ocean in the past. However, it is not clear whether part of this ocean is still present and whether residual fluids are still circulating in the dwarf planet. These fluids may be exposed in a geologically young surface, and the most promising site to verify the occurrence of present fluids on Ceres is Cerealia Facula dome, in Occator crater. This very young facula exhibits minerals that are relatively rare in our Solar System, the formation of which requires the presence of liquid water in combination with hydrothermal activity. Here we report the discovery of hydrated sodium chloride on Cerealia Facula. These newly identified chloride salts are concentrated on the top of the dome, close to a system of radial fractures. The spatial distribution of the hydrated phase suggests that chloride salts are the solid residue of deep brines that reached the surface only recently, or are still ascending. These salts are very efficient in maintaining Ceres’s warm internal temperature and lowering the eutectic temperature of the brines, in which case ascending salty fluids may exist in Ceres today. Spectroscopic data obtained at high spatial resolution from Dawn detected the presence of fresh chloride salts at Cerealia Facula on Ceres. The spatial distribution of the hydration level of these salts suggests that they surfaced a maximum of a few centuries ago and that the upwelling of salty fluids may still be active.

Context.Particulate surfaces exhibit a surge of reflectance at low phase angles, a phenomenon referred to as the opposition effect (OE). Two mechanisms are recognized as responsible for the OE: shadow hiding (SH) and coherent backscattering. The latter is typically characterized by a small angular width of a few degrees at most and according to the theoretical prediction should exhibit wavelength and albedo dependence.Aims.We characterize the OE on the surface of Ceres using Dawn Visible InfraRed mapping spectrometer hyperspectral images at low phase angles. Furthermore, this dataset, coupled with previous observations, allows us to perform a complete spectrophotometric modeling at visual-to-infrared (VIS-IR) wavelengths (0.465–4.05μm) in the broad phase angle range ≈0°−132°.Methods.We applied Hapke’s theory to the average phase curve for Ceres. Disk-resolved properties of the OE were investigated through an empirical model.Results.Across the investigated phase angle interval, Ceres’ average phase curve exhibits a smaller back-scattering contribution for increasing wavelengths. This determines a progressive spectral reddening at larger phase angles that we hypothesize as being related to the effect of submicron roughness on the grain surface. In the OE region, the shape of the phase curves is fairly constant across the VIS range and no sharp opposition surge at very small phase angles (α< 2°) can be recognized. This would suggest a major contribution from SH to Ceres’ OE. Assuming SH as the dominant mechanism, from the OE angular width we infer a high surface porosity (≈0.9), which appears in good qualitative agreement with Ceres’ low thermal inertia. Thanks to the OE observations we derive Ceres’ VIS-IR geometric albedo with a reference value at 0.55μm of 0.098 ± 0.007. Mapping of the VIS normal albedo and OE angular width across a portion of the surface of Ceres does not reveal a spatial correlation between these quantities, consistent with SH dominating in theα= 0°−7° interval. The comparison of Ceres’V-band magnitude curve with that of other asteroids indicates that Ceres’ OE is typical of a low-albedo object and compatible with the C-class type.

Full list of authors: Cremonese, G.; Capaccioni, F.; Capria, M. T.; Doressoundiram, A.; Palumbo, P.; Vincendon, M.; Massironi, M.; Debei, S.; Zusi, M.; Altieri, F.; Amoroso, M.; Aroldi, G.; Baroni, M.; Barucci, A.; Bellucci, G.; Benkhoff, J.; Besse, S.; Bettanini, C.; Blecka, M.; Borrelli, D.; Brucato, J. R.; Carli, C.; Carlier, V.; Cerroni, P.; Cicchetti, A.; Colangeli, L.; Dami, M.; Da Deppo, V.; Della Corte, V.; De Sanctis, M. C.; Erard, S.; Esposito, F.; Fantinel, D.; Ferranti, L.; Ferri, F.; Ficai Veltroni, I.; Filacchione, G.; Flamini, E.; Forlani, G.; Fornasier, S.; Forni, O.; Fulchignoni, M.; Galluzzi, V.; Gwinner, K.; Ip, W.; Jorda, L.; Langevin, Y.; Lara, L.; Leblanc, F.; Leyrat, C.; Li, Y.; Marchi, S.; Marinangeli, L.; Marzari, F.; Mazzotta Epifani, E.; Mendillo, M.; Mennella, V.; Mugnuolo, R.; Muinonen, K.; Naletto, G.; Noschese, R.; Palomba, E.; Paolinetti, R.; Perna, D.; Piccioni, G.; Politi, R.; Poulet, F.; Ragazzoni, R.; Re, C.; Rossi, M.; Rotundi, A.; Salemi, G.; Sgavetti, M.; Simioni, E.; Thomas, N.; Tommasi, L.; Turella, A.; Van Hoolst, T.; Wilson, L.; Zambon, F.; Aboudan, A.; Barraud, O.; Bott, N.; Borin, P.; Colombatti, G.; El Yazidi, M.; Ferrari, S.; Flahaut, J.; Giacomini, L.; Guzzetta, L.; Lucchetti, A.; Martellato, E.; Pajola, M.; Slemer, A.; Tognon, G.; Turrini, D. -- This is an open access article, The SIMBIO-SYS (Spectrometer and Imaging for MPO BepiColombo Integrated Observatory SYStem) is a complex instrument suite part of the scientific payload of the Mercury Planetary Orbiter for the BepiColombo mission, the last of the cornerstone missions of the European Space Agency (ESA) Horizon + science program. The SIMBIO-SYS instrument will provide all the science imaging capability of the BepiColombo MPO spacecraft. It consists of three channels: the STereo imaging Channel (STC), with a broad spectral band in the 400-950 nm range and medium spatial resolution (at best 58 m/px), that will provide Digital Terrain Model of the entire surface of the planet with an accuracy better than 80 m; the High Resolution Imaging Channel (HRIC), with broad spectral bands in the 400-900 nm range and high spatial resolution (at best 6 m/px), that will provide high-resolution images of about 20% of the surface, and the Visible and near-Infrared Hyperspectral Imaging channel (VIHI), with high spectral resolution (6 nm at finest) in the 400-2000 nm range and spatial resolution reaching 120 m/px, it will provide global coverage at 480 m/px with the spectral information, assuming the first orbit around Mercury with periherm at 480 km from the surface. SIMBIO-SYS will provide high-resolution images, the Digital Terrain Model of the entire surface, and the surface composition using a wide spectral range, as for instance detecting sulphides or material derived by sulphur and carbon oxidation, at resolutions and coverage higher than the MESSENGER mission with a full co-alignment of the three channels. All the data that will be acquired will allow to cover a wide range of scientific objectives, from the surface processes and cartography up to the internal structure, contributing to the libration experiment, and the surface-exosphere interaction. The global 3D and spectral mapping will allow to study the morphology and the composition of any surface feature. In this work, we describe the on-ground calibrations and the results obtained, providing an important overview of the instrument performances. The calibrations have been performed at channel and at system levels, utilizing specific setup in most of the cases realized for SIMBIO-SYS. In the case of the stereo camera (STC), it has been necessary to have a validation of the new stereo concept adopted, based on the push-frame. This work describes also the results of the Near-Earth Commissioning Phase performed few weeks after the Launch (20 October 2018). According to the calibration results and the first commissioning the three channels are working very well. © 2020, The Author(s)., We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0. The SIMBIO-SYS instrument has been developed by Leonardo under ASI contract I/054/10/0.

International audience; K nowledge of the surface temperature distribution of a comet's nucleus proves to be of fundamental importance for a number of reasons: the evaluation of the thermophysical properties (thermal inertia and roughness, at several spatial scales), the characterization of the thermal behaviour of peculiar surface units (for example, local ice exposures, or inherently cold material units not to be confused with shaded areas), and for the understanding of the physical processes affecting the surface and the shallow subsur-face layers (for example, sublimation of volatile compounds). The distribution of surface temperatures of a cometary nucleus, closely measured by a spacecraft, can be compared with theoretical models meant to predict the thermophysical properties of the nucleus at various depths and with previous thermal observations carried out by both Earth-based and space-based telescopes, with the goal of validating and/or improving those models 1. Furthermore, the temporal evolution of the surface temperatures, primarily driven by insolation, is critical in triggering the activity of a comet, allowing the migration of volatile compounds from the interior of the nucleus and the production of gas and dust observable with different techniques 2. In the past, thermal surveys of minor bodies were carried out using ground-based and space-based facilities. However, due to the limited spatial resolution of those observations, in most cases the derived thermal properties were only global averages, and the determined temperatures were highly model dependent. Before Rosetta, direct measurements of cometary nuclei surface temperatures were obtained during short periods for a handful of comets, namely 1P/ Halley 3 , 19P/Borrelly 4 , 9P/Tempel 1 1 and 103P/Hartley 2 5 , with a maximum spatial resolution of approximately 30 m per pixel. Here we study the surface temperature distribution of the nucleus of comet 67P/Churyumov-Gerasimenko as derived by the Visible InfraRed and Thermal Imaging Spectrometer, Mapping channel (VIRTIS-M, hereafter VIRTIS) 6 in Rosetta's early global mapping phase after comet encounter. These data cover the pre-perihelion period from 1 August to 23 September 2014, when the heliocentric distance decreased from 3.62 to 3.31 au and the spacecraft was in the altitude range 61-13 km above the surface, resulting in a spatial resolution from approximately 15 to 3 m per pixel (most data showing a resolution of 13 to 15 m per pixel). In this period, the solar phase angle ranged from 17° to 93°, which Knowledge of the surface temperature distribution on a comet's nucleus and its temporal evolution at different timescales is key to constraining its thermophysical properties and understanding the physical processes that take place at and below the surface. Here we report on time-resolved maps of comet 67P/Churyumov-Gerasimenko retrieved on the basis of infra-red data acquired by the Visible InfraRed and Thermal Imaging Spectrometer (VIRTIS) onboard the Rosetta orbiter in 2014, over a roughly two-month period in the pre-perihelion phase at heliocentric distances between 3.62 and 3.31 au from the Sun. We find that at a spatial resolution ≤15 m per pixel, the measured temperatures point out the major effect that self-heating, due to the complex shape of the nucleus, has on the diurnal temperature variation. The bilobate nucleus of comet 67P also induces daytime shadowing effects, which result in large thermal gradients. Over longer periods, VIRTIS-derived temperature values reveal seasonal changes driven by decreasing heliocentric distance combined with an increasing abundance of ice within the uppermost centimetre-thick layer, which implies the possibility of having a largely pristine nucleus interior already in the shallow subsurface.

High-resolution mapping of Ceres, Vesta and the icy satellites of Saturn, Uranus and Pluto reveals a rich variety of well-preserved impact crater morphologies on these low gravity bodies. These objects provide a natural laboratory to study effects of composition on crater formation processes under similar surface gravity conditions (though mean impact velocities vary by several factors). Simple craters occur on all these bodies but subtle differences in morphology on Ceres and Vesta are recognized. Immature complex craters (with large floor mounds but not terraces or conical central peaks) occur on Vesta and while smaller than predicted are consistent with its silicate composition. Asymmetric simple craters (with incomplete scarp development) on all bodies are likely related to differential overburden stresses in the rim, and their occurrence is consistent with lower crustal strength on icy bodies including Ceres. Immature and mature complex craters exhibit increasing degrees of complexity, including spiral floor deformation patterns (related to failure in converging floor material), central peaks, and impact melt. Cerean crater morphologic types and simple-complex transition diameters are smaller than on Vesta but similar to those on icy satellites, indicating a much weaker rheology for Ceres' outer layers under impact conditions. These are consistent with geophysical indications of a low-density water ice and probably clathrate rich outer shell. Fluidized floor deposits (impact melt or melt-solid mixtures) are significant in craters >25 km across on Ceres but absent on Saturn satellites. Central pit craters are common on Ceres (at diameters of ~75 to 150 km consistent with gravity scaling from the larger Galilean satellites) but are absent on Saturnian satellites and Charon. The contrasting impact melt and central pit behaviors on Ceres and Saturn's moons is contrary to expectation given the higher impact velocities at Saturn but might be related to lower internal temperatures, or the higher fraction of non-ice material on Ceres. The correlation or scaling of transition diameters to surface gravity is near −0.65 rather than −1, perhaps due to increased porosity on lower gravity bodies. The fundamental similarity of crater morphologies on Ceres and icy satellites, however, indicates that the weaker rheology of water ice results in similar craters even if the non-(ice+clathrate) components are as high as ~30 vol%.

A recent study of Fu et al. analysed the remaining magnetization in the eucrite meteorite Allan Hills A81001, which mostly likely has been produced during the cooling phase of the life of the asteroid Vesta, arguing that an ancient dynamo in the advective liquid metallic core could be set in. Using petrographic and paleomagnetic arguments, Fu et al. estimated a surface magnetic field of at least 2 μT. In this work, we verify the possibility that an early core dynamo took place in Vesta by analysing four different possible fully differentiated configurations of Vesta, characterized by different chondritic compositions, with the constraints on core size and density provided by Ermakov et al. We only incorporate the thermal convection, by neglecting the effects of the compositional convection, so our results in terms of magnetic Reynolds number and duration of the dynamo can be interpreted as a lower bound. The presence of a magnetic field would make Vesta a peculiar object of the Solar system, a `small-Earth', since it has also a differentiated structure like Earth and the magnetic field has preserved Vesta from the space weathering.

Spectral parameters of Ceres measured by the Dawn/VIR imaging spectrometer are studied as a function of illumination angles, by applying a semi-empirical method based on a statistical analysis of the VIR dataset acquired up to September 2016. The study also focuses on the photometry of the Occator faculae, i.e. the brightest spots of the Ceres surface, showing an albedo up to eight times the Ceres average. The considered semi-empirical approach takes into account the small extension (and hence small dataset) of this region and lays the groundwork to apply scattering models even on such a limited area. The behavior of Ceres visible and infrared reflectance with phase angle is similar to other asteroids belonging to its same spectral class, i.e. C-type. The depth of the bands at 2.7 µm (phyllosilicates), 3.1 µm (ammonium), 3.4 µm (magnesium carbonates) and the infrared spectral slope linearly increase with phase angle, showing analogies with other asteroids and occurrence of phase reddening. The different behavior of the 3.9 µm band depth (also due to Mg carbonates), independent of illumination angles, could indicate that other carriers contribute to the 3.4 µm band and play a more important role in photometry outside the carbonate deposits. The phase function of the Occator faculae is much steeper than expected from its high albedo. Mixture of bright and dark material and larger roughness can be at the basis of this result. The phyllosilicate bands show a steeper increase with phase angle with respect to the Ceres average, due to the lower presence of dark materials, and/or again larger roughness. The absence of trends with phase angles of the two carbonate bands and of the spectral slope suggests that carbonates do not produce phase reddening.

The goal of the ESA Luna 27/PROSPECT instrument [1] is to extract and characterize a regolith sample from the lunar south polar region, investigating its physical and chemical properties. The main target is to characterize the abundance and distribution of water ice and other volatiles so the challenge is to preserve volatiles in samples during the drilling transfer and analysis. In this work we provided numerical simulations in order to predict the expected ice sublimation rates and inform the system's development. Simulations are characterized by different initial boundary conditions as well as thermodynamic parameters and carried out on a cylinder representing a lunar regolith sample of the south polar region.

The Ceres surface is globally composed of Mg-phyllosilicates, ammoniated clays, carbonates and dark components. To obtain a more detailed mineralogical and geological investigation, the dwarf planet surface has been divided into fifteen quadrangles. The aim of this work is to investigate the abundance of phyllosilicates and ammoniated clays in the Kerwan quadrangle, classified as Ac-H-7 and spanning from 22°S to 22°N in latitude and from 72°E to 144°E in longitude. Maps of band depth distribution at 2.7 µm and 3.1 µm have been performed and compared with a map of geometric albedo estimated at 1.2 µm. Phyllosilicates and ammoniated clays generally correlate in the Kerwan quadrangle, even if departure from this behavior is observed in the floor of Kerwan, Inamahari and Homsuk craters. The greatest abundance of ammoniated phyllosilicates is found in Rao and Kerwan ejecta, while Bonsu and Tafakula floors are the most depleted in volatile, as well as Inamahari and Dantu ejecta. Six bright spots are detected in the Kerwan quadrangle, and the one richest in carbonate is related to Dantu ejecta in the southeast region. Some younger features (such as Rao or Kerwan ejecta) show deeper band depths than older terrain, a contrast trend with respect to the entire Ceres surface. Since this correlation is observed in a few other places on other quadrangles but not on the entire Ceres surface, it is possible that recent impact events could have been masked this correlation.

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Open Access funding provided by Max Planck Society., On 27 April 2015, when comet 67P/Churyumov-Gerasimenko was at 1.76 au from the Sun and moving toward perihelion, the OSIRIS and VIRTIS-M instruments on board the Rosetta spacecraft simultaneously observed the evolving dust and gas coma during a complete rotation of the comet.© C. Tubiana et al. 2019, OSIRIS was built by a consortium led by the Max-Planck-Institut fur Sonnensystemforschung, Gottingen, Germany, in collaboration with CISAS, University of Padova, Italy, the Laboratoire d'Astrophysique de Marseille, France, the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain, the Scientific Support Office of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, the Universidad Politechnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut fur Daten-technik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the Rosetta Science Ground Segment at ESAC, the Rosetta Mission Operations Centre at ESOC and the Rosetta Project at ESTEC for their outstanding work enabling the science return of the Rosetta Mission. VIRTIS was built by a consortium, which includes Italy, France, and Germany, under the scientific responsibility of the Istituto di Astrofisica e Planetologia Spaziali of INAF, Italy, which also guides the scientific operations. The VIRTIS instrument development, led by the prime contractor Leonardo-Finmeccanica (Florence, Italy), has been funded and managed by ASI, with contributions from Observatoire de Meudon financed by CNES, and from DLR. We thank the Rosetta Science Ground Segment and the Rosetta Mission Operations Centre for their support throughout all the phases of the mission. The VIRTIS calibrated data will be available through the ESA's Planetary Science Archive Website (www.rssd.esa.int) and is available upon request until posted to the archive. We thank the following institutions and agencies for support of this work: Italian Space Agency (ASI, Italy) contract number I/024/12/1, Centre National d'Etudes Spatiales (CNES, France), DLR (Germany), NASA (USA) Rosetta Program, and Science and Technology Facilities Council (UK).

Recent space-based observations have revealed or suggested the existence of various types of carbonate salts in several Solar System bodies, such as Mars, Ceres, Enceladus, and Europa. Natrite is the main component of the crater Occator's faculae observed in detail by the Dawn spacecraft on the dwarf planet Ceres. Sodium carbonates are thought to form as precipitates in brines, originating in aqueous environments in the subsurface of Ceres and icy bodies. Here we report about near-infrared (0.8-4.2 μm) reflectance spectroscopic investigations on three compounds, namely natrite (anhydrous Na2CO3), monohydrated sodium carbonate (Na2CO3∙H2O, thermonatrite) and decahydrate sodium carbonate (Na2CO3∙10H2O, natron). Spectral measurements have been carried out in the overall temperature range 93-279 K, representative of planetary surfaces. The analysis of diagnostic spectral signatures shows different temperature-dependent trends for several band parameters, as well as different behavior as a function of the grain size for a given temperature. While spectra of natrite are characterized by several CO3 absorptions, broad and strong absorption features due to H2O dominate the spectra of heavily hydrated natron. The intermediate sample (monohydrated) shows multiple bands due to the overlap of CO3 and H2O vibrational modes. Our temperature-dependent laboratory spectra are compared with Dawn-VIR spectra of Ceres and with Galileo-NIMS spectra of Europa.

We analyze 2–5μm spectroscopic observations of the dust coma of comet 67P/Churyumov-Gerasimenko obtained with the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-H) instrument on board Rosetta from 3 June to 29 October 2015 at heliocentric distancesrh= 1.24–1.55 AU. The 2–2.5μm color, bolometric albedo, and color temperature were measured using spectral fitting. Data obtained atα= 90° solar phase angle show an increase in bolometric albedo (0.05–0.14) with increasing altitude (0.5–8 km), accompanied by a possible marginal decrease in color and color temperature. Possible explanations include dark particles on ballistic trajectories in the inner coma and radial changes in particle composition. In the phase angle range 50°–120°, phase reddening is significant (0.031%/100 nm deg−1) for a mean color of 2%/100 nm atα= 90°, which might be related to the roughness of the dust particles. Moreover, a decrease in color temperature with decreasing phase angle is also observed at a rate of ~0.3 K deg−1, consistent with the presence of large porous particles, with low thermal inertia, and showing a significant day-to-night temperature contrast. Comparing data acquired at fixed phase angle (α= 90°), a 20% increase in bolometric albedo is observed near perihelion. Heliocentric variations in dust color are not significant in the time period we analyzed. The measured color temperatures vary from 260 to 320 K, and follow arh−0.6variation in therh= 1.24–1.5 AU range, which is close to the expectedrh−0.5value.

Mapping Ceres’ surface composition in the Dantu region, located between 21°–66°N and 90°–180°E, offers the unique possibility to investigate changes in the surface composition related to different stratigraphic levels of Ceres’ crust. Dantu is located in a huge depression named Vendimia Planitia, which possibly represents a completely degraded impact basin formed in the beginning of Ceres’ geological history. Most parts of this depression are characterized by strong phyllosilicate absorptions, which are stronger than elsewhere on Ceres’ surface. This spectral signature possibly is related to the material emplaced at the time of the Vendimia impact event excavating material from deeper regions of Ceres’ crust. Subsequent impacts in this basin reach far deeper into Ceres’ crust than any impact events outside of Vendemia Planitia, which could explain the spectral signature of Dantu, possibly pointing to a higher concentration of ammonium-bearing phyllosilicates in Ceres’ deeper crust. Spectral differences with respect to the small fresh craters on Dantu's floor are probably related to grain size effects causing a bluish visible slope as observed by fresh impact craters on other places on Ceres. The local enrichment of carbonates in the Dantu area could also be associated with the impact event and may have been formed by additional impact-triggered and/or post-impact alteration processes.

The results of the in situ exploration of the asteroid (4) Vesta by the Dawn spacecraft open new perspectives in the field of interpretation of remote-sensing polarimetric measurements of asteroids. (4) Vesta has long been known to be the only asteroid exhibiting a cyclic variation of the degree of linear polarization of the sunlight scattered by its surface, with a period which is synchronous with the object's rotation. This variation must be the consequence of some heterogeneity of the asteroid's surface, including regions characterized by different albedo, or composition, or regolith properties, or a combination of the above features. For a long time, this kind of conclusion has remained essentially qualitative. Now, after the extensive exploration of Vesta's surface by Dawn, it is possible to interpret the data set of polarimetric measurements of Vesta, including some unpublished data presented here for the first time, in terms of a correspondence between the degree of linear polarization and the variation of local properties of the surface visible to ground-based observers during Vesta's rotation, as seen at different epochs and under different illumination conditions. This makes it possible to refine our knowledge of the empirical relation between polarization properties and albedo, which is commonly used to derive the albedo from remote-sensing measurements of linear polarization of atmosphereless Solar system bodies. Fil: Cellino, A.. Istituto Nazionale Di Astrofisica; Italia. Osservatorio Astrofisico di Torino; Italia Fil: Ammannito, E.. University of California at Los Angeles; Estados Unidos Fil: Magni, G.. Istituto Nazionale Di Astrofisica; Italia Fil: Gil Hutton, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentina Fil: Tedesco, E. F.. Planetary Science Institute; Estados Unidos Fil: Belskaya, I. N.. Kharkiv National University. Institute of Astronomy; Ucrania Fil: De Sanctis, M. C.. Istituto Nazionale Di Astrofisica; Italia Fil: Schröder, S.. DLR Institute of Planetary Research; Alemania Fil: Preusker, F.. DLR Institute of Planetary Research; Alemania Fil: Manara, A.. Istituto Nazionale Di Astrofisica; Italia. Osservatorio Astronomico di Brera; Italia

Recent observations of water emission around Ceres suggest the presence of an ice layer on or beneath the surface of this asteroid. Several mechanisms have been suggested to explain these plumes, among which cometary-like sublimation seems to be plausible, since there is a correlation between the magnitude of the emission and the change in the heliocentric distance along the orbit. In this work, we applied a comet sublimation model to study the plausible scenarios that match with Herschel observations of the water flux (1026 molecules s-1). Each scenario is characterized by a well-defined set of physical and orbital parameters. Moreover, a study of the dynamic evolution of the H2O plume has been performed, showing that an optically thin transient atmospheric envelope, with a typical timescale of some tens of days, can be maintained by the H2O surface emission. Our simulations could be useful theoretical support for the Dawn NASA mission by giving a better understanding of the physical conditions for water sublimation and ice stability.

The Av-13 (Tuccia) and Av-14 (Urbinia) quadrangles are located in the south-west region of Vesta. They are characterized by a large topographic variability, from the highest (Vestalia terra highlands) to the lowest (Rheasilvia basin). Many geological units in these quadrangles are not associated with mineralogical variability, as shown by the color-composite maps. Maps of mafic absorption band-center position reveal that the principal lithology is eucrite-rich howardite, but diogenite-rich howardite areas are also present, corresponding to particular features such as Antonia and Justina craters, which are characterized by strong mafic absorptions. These quadrangles, especially Urbinia, contain many bright ejecta, such as those of Tuccia crater, which are the highest reflectance materials on Vesta (Zambon et al., 2014). Dark areas are present and correspond to regions with deeper OH-signature. The two quadrangles contain many vertical ridge crests associated with the Rheasilvia impact. These ridges do not show mineralogical differences with respect to their surroundings, but have a distinctive appearance in color-ratio composite images.

The equatorial Marcia quadrangle region is characterized by the large, relatively young impact craters Marcia and Calpurnia and their surrounding dark ejecta field, a hill with a dark-rayed crater named Aricia Tholus, and an unusual diffuse material surrounding the impact crater Octavia. The spectral analysis indicates that while this region is relatively uniform in the pyroxene band centers, it instead shows large differences in pyroxene band depths and reflectance. A large variation of reflectance is seen in the quadrangle: bright and dark materials are present as diffuse material, and as concentrated spots and outcrops. Moreover, OH signature is pervasive in the quadrangle, with a few exceptions. The region, especially the Marcia ejecta field, is characterized by spectra showing the 2 μm band shifted at long wavelengths. This is commonly associated with eucritic material, believed to have crystallized as lava on Vesta’s surface or within relatively shallow-level dikes and plutons, thus suggesting that this region is a remnant of the old Vestan basaltic crust. However, other characteristics of the spectra do not fully fit the eucritic composition, indicating an alternative explanation for the band center distribution, including the presence of carbonaceous chondritic material mixed with the native Vestan pyroxene. The detailed mineralogical analysis of the Marcia quadrangle indicates that this quadrangle is the result of the mixture of the Vestan “endogenic” minerals with the “exogenic” carbonaceous chondrites. The stratigraphic units around Marcia clearly show the bright, uncontaminated material interlaced and mixed with the dark material that contains a strong OH signature. Only few small areas can be considered as representative of the old Vestan original material.

Here we present the spectral parameter maps used in this Surface Composition of Vesta Special Issue. The use of spectral parameters have been important since the first ground-based observations of Vesta as they can describe single mineralogic aspects as abundances or change in surface composition. Mapping these parameters over the surface shows the mineralogic diversity across the asteroid Vesta. In this work we discuss the development of the maps, which are produced from the data of the Visible and Infrared mapping spectrometer onboard NASA’s Dawn mission. We describe how we processed the VIR spectra and how we produced the geometries of data acquisition. Spectra and geometries are used to design a Geographic Information System procedure to mosaic these data. We conclude the article with a description of the trends of the pyroxene-related spectral parameters across the asteroid, and some statistics on the spectral parameters of each map within the quadrangle-based scheme used in this special issue.

The future ExoMars rover mission (ESA/Roscosmos), to be launched in 2018, will investigate the habitability of the Martian surface and near subsurface, and search for traces of past life in the form of textural biosignatures and organic molecules. In support of this mission, a selection of relevant Mars analogue materials has been characterised and stored in the International Space Analogue Rockstore (ISAR), hosted in Orléans, France. Two ISAR samples were analysed by prototypes of the ExoMars rover instruments used for petrographic study. The objective was to determine whether a full interpretation of the rocks could be achieved on the basis of the data obtained by the ExoMars visible-IR imager and spectrometer (MicrOmega), the close-up imager (CLUPI), the drill infrared spectrometer (Ma-Miss) and the Raman spectrometer (RLS), first separately then in their entirety. In order to not influence the initial instrumental interpretation, the samples were sent to the different teams without any additional information. This first step was called the "Blind Test" phase. The data obtained by the instruments were then complemented with photography of the relevant outcrops (as would be available during the ExoMars mission) before being presented to two geologists tasked with the interpretation. The context data and photography of the outcrops and of the samples were sufficient for the geologists to identify the rocks. This initial identification was crucial for the subsequent, iterative interpretation of the spectroscopic data. The data from the different spectrometers was, thus, cross-calibrated against the photographic interpretations and against each other. In this way, important mineralogical details, such as evidence of aqueous alteration of the rocks, provided relevant information concerning potential habitable conditions. The final conclusion from this test is that, when processed together, the ExoMars payload instruments produce complementary data allowing reliable interpretation of the geological context and potential for habitable environments. This background information is fundamental for the analysis and interpretation of organics in the processed Martian rocks. © 2015 Elsevier Ltd. All rights reserved.

The dwarf planet Ceres has been explored by NASA's Dawn spacecraft with the goal of characterizing its geology, mineralogy, topography, shape, and internal structure. One outcome of this exploration is the production of geologic maps, meant to unveil the geologic history of Ceres. In this paper, we present the geologic map of the Ac-6 Haulani quadrangle (Lat. 22°S-22°N, Long. 0°–72°E) based on Low Altitude Mapping Orbit (LAMO) (∼35 m/pixel) data supplemented with color and spectral data, as well as a digital terrain model from the High Altitude Mapping Orbit (HAMO) (∼135 m/pixel, vertical accuracy of about 10 m). The 34 km diameter Haulani crater is one of the youngest features on Ceres and the most prominent one in the quadrangle. Haulani was formed on a topographical transition in north–south direction and shows a complex morphology with a variety of lobate flows and tectonic features. Multiple cracks and depressions around the crater indicate the failure of subsurface material. These were likely formed by the subsidence of material due to the instability of the subsurface. The mapping of Ac-6 Haulani suggests that Ceres is built up of layers with different material properties. We propose that Ceres has a solid crust and a variable ice-rich subsurface consistent with previous and recent models of Ceres' interior.

The Dawn Science Team is conducting a geological mapping campaign at Ceres during the nominal mission, including iterative mapping using data obtained during each orbital phase. We are using geological mapping as a method to identify the geologic processes that have modified the surface of dwarf planet Ceres. We here present the geology of the Ac-9 Occator quadrangle, located between 22˚S-22˚N and 216-288˚E. The Ac-9 map area is within the topographically high region named Hanami Planum. Features of note within the profile include impact craters Occator, Azacca, Lociyo, Nepen and Kirnis. Four of these craters have fractured, shallow floors, morphometrically comparable to floor-fractured craters (FFCs) on the Moon. Similar to models for the formation of the lunar FFCs, we suggest that these Ceres FFCs are a result of cryomagmatic uplift under the crater floors. A set of regional linear structures called the Samhain Catenae do not have any obvious relationship to impact craters. Many of the catenae are comprised of smaller structures that have linked together, suggestive of en echelon fractures. It has been suggested that these fractures formed due to the uplift of Hanami Planum due to cryromagmatic plumes.

We report on a preliminary global geologic map of Vesta, based on data from the Dawn spacecraft’s High-Altitude Mapping Orbit (HAMO) and informed by Low-Altitude Mapping Orbit (LAMO) data. This map is part of an iterative mapping effort; the geologic map has been refined with each improvement in resolution. Vesta has a heavily-cratered surface, with large craters evident in numerous locations. The south pole is dominated by an impact structure identified before Dawn’s arrival. Two large impact structures have been resolved: the younger, larger Rheasilvia structure, and the older, more degraded Veneneia structure. The surface is also characterized by a system of deep, globe-girdling equatorial troughs and ridges, as well as an older system of troughs and ridges to the north. Troughs and ridges are also evident cutting across, and spiraling arcuately from, the Rheasilvia central mound. However, no volcanic features have been unequivocally identified. Vesta can be divided very broadly into three terrains: heavily-cratered terrain; ridge-and-trough terrain (equatorial and northern); and terrain associated with the Rheasilvia crater. Localized features include bright and dark material and ejecta (some defined specifically by color); lobate deposits; and mass-wasting materials. No obvious volcanic features are evident. Stratigraphy of Vesta’s geologic units suggests a history in which formation of a primary crust was followed by the formation of impact craters, including Veneneia and the associated Saturnalia Fossae unit. Formation of Rheasilvia followed, along with associated structural deformation that shaped the Divalia Fossae ridge-and-trough unit at the equator. Subsequent impacts and mass wasting events subdued impact craters, rims and portions of ridge-and-trough sets, and formed slumps and landslides, especially within crater floors and along crater rims and scarps. Subsequent to the formation of Rheasilvia, discontinuous low-albedo deposits formed or were emplaced; these lie stratigraphically above the equatorial ridges that likely were formed by Rheasilvia. The last features to be formed were craters with bright rays and other surface mantling deposits. Executed progressively throughout data acquisition, the iterative mapping process provided the team with geologic proto-units in a timely manner. However, interpretation of the resulting map was hampered by the necessity to provide the team with a standard nomenclature and symbology early in the process. With regard to mapping and interpreting units, the mapping process was hindered by the lack of calibrated mineralogic information. Topography and shadow played an important role in discriminating features and terrains, especially in the early stages of data acquisition.

Deposits of dark material appear on Vesta’s surface as features of relatively low-albedo in the visible wavelength range of Dawn’s camera and spectrometer. Mixed with the regolith and partially excavated by younger impacts, the material is exposed as individual layered outcrops in crater walls or ejecta patches, having been uncovered and broken up by the impact. Dark fans on crater walls and dark deposits on crater floors are the result of gravity-driven mass wasting triggered by steep slopes and impact seismicity. The fact that dark material is mixed with impact ejecta indicates that it has been processed together with the ejected material. Some small craters display continuous dark ejecta similar to lunar dark-halo impact craters, indicating that the impact excavated the material from beneath a higher-albedo surface. The asymmetric distribution of dark material in impact craters and ejecta suggests non-continuous distribution in the local subsurface. Some positive-relief dark edifices appear to be impact-sculpted hills with dark material distributed over the hill slopes. Dark features inside and outside of craters are in some places arranged as linear outcrops along scarps or as dark streaks perpendicular to the local topography. The spectral characteristics of the dark material resemble that of Vesta’s regolith. Dark material is distributed unevenly across Vesta’s surface with clusters of all types of dark material exposures. On a local scale, some craters expose or are associated with dark material, while others in the immediate vicinity do not show evidence for dark material. While the variety of surface exposures of dark material and their different geological correlations with surface features, as well as their uneven distribution, indicate a globally inhomogeneous distribution in the subsurface, the dark material seems to be correlated with the rim and ejecta of the older Veneneia south polar basin structure. The origin of the dark material is still being debated, however, the geological analysis suggests that it is exogenic, from carbon-rich low-velocity impactors, rather than endogenic, from freshly exposed mafic material or melt, exposed or created by impacts.